1. Field of the Invention
The present invention relates to a vehicle body vibration control device for a vehicle such as an automobile, and more particularly, to a vehicle body vibration control device configured to suppress vibration of a vehicle body, which is caused by fluctuation in driving force of the vehicle.
2. Description of the Related Art
Vehicles such as automobiles travel by a driving force generated by a driving unit such as an engine. Fluctuation in driving force generated from the driving unit causes loads to be applied on the vehicle body in a fore-and-aft direction and a vertical direction of the vehicle relative to wheels. Thus, pitching vibration occurs in the vehicle body. Therefore, it has been suggested that the pitching vibration of the vehicle body be reduced through appropriate control of a command driving force to the driving unit.
For example, Japanese Patent Application Laid-open No. 2007-237879 filed by the applicant of this application describes a vehicle body vibration control device configured based on the above-mentioned concept. This vehicle body vibration control device includes a request driving force calculation unit configured to calculate a driver's request driving force, a driving unit configured to apply a driving force to a vehicle, a driving force control unit configured to control the driving unit based on a command driving force, and a notch filter configured to receive a signal indicating the request driving force from the request driving force calculation unit. The notch filter has a notch frequency set to a value for reducing a frequency component of vibration of a vehicle body. The notch filter subjects the signal to filter processing, and outputs the processed signal to the driving force control unit as a signal indicating the command driving force.
According to the vehicle body vibration control device of this type, the signal indicating the driver's request driving force is processed by the notch filter, and the driving unit is controlled based on the command driving force reduced in frequency component of the vibration of the vehicle body. As a result, the pitching vibration of the vehicle body can be reduced.
The driver of the vehicle performs a shifting operation when trying to change the presence or absence of the vehicle driving force or to increase or decrease the driving force. The driver experiences a change of a vehicle speed or a change of an inertial force applied on the driver himself/herself, to thereby confirm a change of the vehicle driving force as expected to be achieved through the shifting operation (moderation feeling concerning driving force).
However, when the signal indicating the request driving force is processed by the notch filter to reduce the vibration of the vehicle body, the driver's request driving force is smoothed through the filter processing to generate the command driving force. Consequently, responsiveness of the driving force of the vehicle to the request driving force is reduced. For example, during acceleration, in other words, during increase of the request driving force, the command driving force is controlled to a smaller side compared to the request driving force. Conversely, during deceleration, in other words, during decrease of the request driving force, the command driving force is controlled to a larger side compared to the request driving force. Thus, the driver experiences a change of the vehicle speed or a change of the inertial force different from that expected to be achieved through the shifting operation. As a result, the driver may feel uncomfortable.
Depending on the vehicles, the driver may select a vehicle traveling mode through a switching operation or the like. For example, as vehicle traveling modes, there are a normal mode in which the responsiveness of the driving force is set to normal responsiveness, a power mode in which the responsiveness of the driving force is set to high responsiveness, and an eco-mode in which the responsiveness of the driving force is set to moderate responsiveness. Even when the traveling mode of the vehicle is changed, the driver expects responsiveness of the vehicle driving force corresponding to the change. However, when the driving force is processed through the notch filter, the driver experiences a change of the vehicle speed or a change of the inertial force different from that expected to be achieved through the changing operation for the traveling mode. As a result, the driver may feel uncomfortable.